1. Technical Field
The present invention relates to liquid crystal devices, methods for manufacturing such liquid crystal devices, and electronic apparatuses. The present invention particularly relates to a liquid crystal device in which light sources are prevented from being misaligned with a light guide plate, a method for manufacturing such a liquid crystal device, and an electronic apparatus including such a liquid crystal device.
2. Related Art
Liquid crystal devices are known as electro-optical devices for displaying images. The liquid crystal devices each include a pair of substrates, opposed to each other, having electrodes. The liquid crystal devices display pictures or images including characters in such a manner that voltages are selectively applied to pixels corresponding to intersections of the electrodes and thereby light passing through a liquid crystal material contained in the pixels is modulated.
A transmissive liquid crystal device includes a lighting unit for transmissive display and a liquid crystal panel. The lighting unit includes a flexible printed circuit (FPC) board, a light source such as a light-emitting diode (LED), and a light guide plate. For the thickness or size reduction of the liquid crystal device, the light source is mounted on the FPC board and is placed near the edge of the light guide plate such that light emitted from the light source is guided to the liquid crystal panel.
JP-A-2002-98945 (hereinafter referred to as Patent Document 1) discloses a method for manufacturing a liquid crystal device including an FPC board. In the method, the following steps are combined into one: a step of fixing a light-shielding tape for preventing light from leaking from a light source and a step of fixing a double-faced adhesive tape for bonding a backlight and a liquid crystal panel together. Therefore, the method is efficient.
In particular, a light-shielding double-faced adhesive tape 200 is used in the method. With reference to FIG. 14, the light-shielding double-faced adhesive tape 200 includes a polyethylene terephthalate (PET) film 205 serving as a base, a light-shielding layer 204 lying on a face of the PET film 205, a first adhesive layer 203, and a second adhesive layer 206. The PET film 205 and the light-shielding layer 204 are sandwiched between the first and second adhesive layers 203 and 206. The light-shielding double-faced adhesive tape 200 is sandwiched between a first release sheet 202 and a second release sheet 207. The light-shielding double-faced adhesive tape 200 is used in a step of bonding a liquid crystal panel 210 to a light source unit 212.
Although the liquid crystal panel 210 is bonded to a light source unit 212 including the light source 213 with the light-shielding double-faced adhesive tape 200 and the light source unit 212 is electrically connected to an FPC board 293, no stress is generated in the FPC board 293. As shown in FIG. 15A, the liquid crystal panel 210 can therefore be held flat.
In FIGS. 15A and 15B, in order to provide a clear understanding of the arrangement of stacked members, the light-shielding double-faced adhesive tape 200 is shown so as to be in direct contact with a light source FPC board 217 and a light-reflecting plate or a light-reflecting film 216. However, there is a possibility that the light-shielding double-faced adhesive tape 200 cannot be seen in a sectional view like FIG. 15A or 15B depending on the width of the light-shielding double-faced adhesive tape 200 or the width of an end section (not shown) of a housing 202 in contact with the light-shielding double-faced adhesive tape 200.
In the liquid crystal device disclosed in Patent Document 1, the liquid crystal panel 210 is lifted by bending the FPC board 293 attached to the rear face of the liquid crystal panel 210 as shown in FIG. 15B.
That is, the light-shielding double-faced adhesive tape 200 is released from the liquid crystal panel 210 (particularly from the end section of the housing 202). This causes the light source FPC board 217 to be lifted in the direction indicated by Arrow A in FIG. 15B.
Therefore, the light source 213 is misaligned with a light guide plate 215. This can reduce the amount of light emitted from the light source 213 to the light guide plate 215 or can vary the intensity of light applied to the light guide plate 215. Therefore, the following problem is caused: a problem that the liquid crystal device displays an image with low or nonuniform brightness.
The lift of the light source 213 causes a problem that portions of the light source 213 are seen by observers. This problem is called hot spots.
An opening may be formed in the light-shielding double-faced adhesive tape 200 such that the light-shielding double-faced adhesive tape 200 is prevented from being bonded to the light source unit 212. However, this reduces the light-shielding ability of the light-shielding double-faced adhesive tape 200, that is, this causes the light-shielding double-faced adhesive tape 200 to be useless.
Another light-shielding double-faced adhesive tape having a large width, a large area, and/or high adhesive strength may be used to tightly bond the liquid crystal panel 210 to the end section of the housing 202. However, this does not comply with a requirement that the display area of the liquid crystal panel 210 is maximized. Furthermore, there is a problem in that this light-shielding double-faced adhesive tape is inferior in repairability.
Alternatively, a cover may be provided on the housing 202 such that the liquid crystal panel 210 is prevented from being lifted. However, this does not comply with requirements that the thickness of the liquid crystal device is minimized and the number of components of the liquid crystal device is also minimized.